The invention relates generally to optical systems used in laser printers, and, more particularly, to an optical lens system for correcting linearity errors associated with torsion oscillator mirrors having a sinusoidal scan angle motion.
Torsion oscillators with a mirrored surface are used in laser printers to scan a laser beam bi-directionally across a laser printer drum. Generally, the scan angle of the mirrored surface of the torsion oscillator varies sinusoidally with respect to time. At the angular extremes of the sinusoidal motion—the point at which the scan reverses direction—the rate of change of the scan angle slows to zero. Due to the decreasing rate of angular change at the scan extremes, dots imaged at a constant rate on a photoconductor of a laser printer are more closely spaced together at the scan extremes than in the middle of the scan line, if there is no optical correction of the scanned laser beam. This causes linearity errors at the ends of the scan line which results in unacceptable print defects in a laser printer application.
What is needed, therefore, is an optical system for correcting linearity errors introduced by the sinusoidal scan angle motion produced by a torsion oscillator mirror in a laser printer.